Field
This invention relates to a rechargeable lithium battery having a positive active material layer, a separator, or both
Description of the Related Technology
A rechargeable lithium battery has higher energy density than a lead battery or a nickel cadmium battery and is widely used. However, the rechargeable lithium battery often has a short cycle-life.
Japanese Patent Publication No. 2011-171293 discloses a method of using a high dielectric solvent such as γ-butyrolactone, propylene carbonate, and the like, and simultaneously dissolving a lithium compound such as lithium tetracyanoborate (LiTCB) and the like in the high dielectric solvent. In other words, the lithium compound such as lithium tetracyanoborate (LiTCB) was used as an electrolyte for an electrolyte solution to improve cycle-life.
However, since the lithium compound is often present in a small amount, for example, 0.7 mol/L is dissolved in the high dielectric solvent, the battery cycle-life improvement, for example under a current density of 1 mA/cm2, is insufficient. In addition, the high dielectric solvent may provide insufficient current density. In order to solve this problem, another method of dissolving the lithium compound in a low dielectric solvent such as diethyl carbonate instead of a high dielectric solvent has been considered, but the lithium compound is not soluble in the low dielectric solvent.
In addition, a rechargeable lithium battery has recently been used at an operation voltage of greater than or equal to about 4.3V, but a low operation voltage is needed in a rechargeable lithium battery based on the disclosure in the Japanese Patent Publication No. 2011-171293. This Japanese patent application discloses increasing the operation voltage of a rechargeable lithium battery by using an electrode with a low potential, for example, graphite as a negative electrode. However, the lithium compound is easily decomposed on the negative electrode.
Therefore, given the limited types of solvents and negative electrodes available, increasing the current density and the operation voltage of a rechargeable lithium battery has been difficult.